Compounds containing a bicyclic aza-containing ring systems have been prepared as conformationally restricted dipeptide surrogates for a variety of medically important compounds. In particular, such ring systems are present in angiotensin converting enzyme (ACE) inhibitors, such as Cilazapril.RTM., and in caspase inhibitors, such as inhibitors of interleukin-1 converting enzyme (ICE).
Current methods for synthesizing compounds containing these byciclic aza-containing ring systems have many disadvantages. The typical methods of forming this ring system have been described [EP 94,095, WO 95/35308, WO 97/22619, U.S. Pat. Nos. 5,656,627, 5,716,929 and 5,756,486 and J. P. Kim, et al., Tetrahedron Letters, 38, pp. 4935-4938 (1997)].
These methods involve coupling an appropriately protected amino acid with the appropriately N(1)-protected piperazic acid or ester. After deprotection, the bicyclic system is then formed via an acid chloride coupling at the N(1) position.
The main disadvantages to such methods are the use of expensive reagents and the number of steps required for protection and deprotection making the overall process extremely time consuming. Moreover, these methods are often useful for research purposes but are not amenable to large scale production.
In order to be more commercially feasible, it would be desirable to produce compounds containing a byciclic aza-containing ring system in an easier, less expensive manner than has been previously described.